This invention relates to a spacer for positioning a boost unit for a brake system on a panel that separates an engine compartment from a passenger compartment of a vehicle in a manner to assure the development of a flow path through which air is communicated from an engine compartment and the boost unit.
In brake boosters of a type disclosed in U.S. Pat. No. 4,953,446, pressure differential is created across a wall that separates a vacuum chamber from a control chamber by air communicated from a passenger compartment. The pressure differential acts on the wall to develop an output force corresponding to an input force applied to a control valve. The control valve includes a return spring that urges a plunger toward an atmospheric seat on a poppet member and a seat spring to urge the poppet toward a vacuum seat. The input force is applied to the push rod which compresses the return spring to move the plunger and sequentially allow the seat spring to seat the poppet member on the vacuum seat and the plunger to move away from the poppet member to thereafter allow air to flow to the control chamber. The communication of air through the poppet can create noise during the development of a pressure differential.
In analyzing the operation of brake boosters it was observed that air supplied to a control valve most often is obtained from the passenger compartment of a vehicle. If the sounds caused by the flow of air from the passenger compartment during the operation of a boost unit could be shifted from the passenger compartment to an engine compartment, a passenger would not hear the booster operation. Unfortunately space in the engine compartment is limited and relocating the brake booster within the engine compartment of a vehicle still requires at least a portion of the components that are associated with a brake booster to remain in a passenger compartment of the vehicle.
The structure illustrated in U.S. Pat. No. 5,487,324 disclosed one way whereby air from the engine compartment may be utilized and supplied to a control chamber of a boost unit to develop the pressure differential during a brake application while the bracket member that offsets the housing of the boost unit into the engine compartment disclosed in U.S. Pat. No. 6,073,535 has a resonant chamber whereby noise is further reduced. The structure in U.S. Pat. No. 6,073,535 functions in an adequate manner when a offset distance is sufficient to provide for the inclusion of a resonant chamber but as may often happen the under hood space available for the boost unit may be limited by other structural components in the engine compartment.
In the present invention, a spacer that positions a boost unit away from a dash panel is mated with a boot to define and maintain a substantially uniform flow path through which air from the engine compartment is presented to a bore that retains a valve during the development of an output force in the boost unit to effect a brake application.